If you value your bike for what you can sell it for, don't even bother with lubing the chain. Chain lube has a poor ROI on an old bike, let alone new wheels, saddle and a bag.
If you value your bike for the pleasure it gives you, then by all means, do things that will improve your pleasure.
Remember, there is no ROI on things that depreciate in value. You cannot "invest" in anything on a bike. It does not appreciate in value. You can certainly spend money on it, but that's an expense, not an investment.